1. Field of the Invention
The present invention relates to an image display device and is applicable, for example, to an active matrix image display device using organic EL (Electro Luminescence) elements. The present invention pulls a power drive signal up to high level at a time other than when a write signal is high. This permits the gray level to be set properly for each pixel circuit even if pixel circuit control using scan lines is shared among a plurality of lines.
2. Description of the Related Art
Recent years have seen the brisk development of active matrix image display devices using organic EL elements as their light-emitting elements. Here, the term “active matrix image display devices using organic EL elements” refer to image display devices which rely on light emission from an organic thin film when the film is applied with an electric field. These elements can be driven by a small voltage of 10 V or less, providing reduced power consumption. Further, these elements are self-luminous. As a result, this type of image display devices may require no backlight, permitting easy reduction of weight and thickness. Further, organic EL elements offer extremely high response speed or approximately several μseconds. As a result, this type of image display devices produces almost no afterimage during display of a moving image.
More specifically, active matrix image display devices using organic EL elements have a display section made up of pixel circuits arranged in a matrix form. Each of the pixel circuits includes an organic EL element and drive circuit adapted to drive the organic EL element. In this type of image display devices, the pixel circuits are driven by a signal drive circuit and scan line drive circuit provided around the display section via signal lines and scan lines provided in the display section to display a desired image.
A method of configuring a pixel circuit using two transistors is disclosed in Japanese Patent Laid-Open No. 2007-310311 (referred to as Patent Document 1 hereinafter) in relation to such an image display device using organic EL elements. Therefore, the method disclosed in Patent Document 1 permits simplification of the configuration of the image display device. Further, a configuration is disclosed in Patent Document 1 which prevents image quality degradation. Image quality degradation is caused by the variations in threshold voltage and mobility of the drive transistor adapted to drive the organic EL element and characteristic changes of the light-emitting element over time.
Japanese Patent Laid-Open No. 2007-133284 (referred to as Patent Document 2 hereinafter) proposes a configuration adapted to correct the variation in threshold voltage of the drive transistor in a plurality of steps. The configuration disclosed in Patent Document 2 makes it possible to assign a sufficient amount of time to the correction of the variation in threshold voltage even in the event that a shorter time is available for setting the gray level of the pixel circuits as a result of precision enhancement. This prevents image quality degradation due to variation in threshold voltage even in the event that improved precision is achieved.